Aim of the work: positron emission tomography (PET) response assessment of residual nodal masses in patients with lymphoma after completion of therapy is performed visually using Douveille as the reference. The primary objective of this study was to define the role of PET in response assessment of Non Hodgkin Lymphoma patients and define various response criteria. Patients and methods: our prospective study included 40 patients with Non Hodgkin's lymphoma diffuse large B cell type assessed for response assessment after completion of therapy, two readers independently assessed response by IHP and Deauville criteria. The addition of morphological parameters on CT was assessed in relation to therapy response. Results: Non Hodgkin lymphoma is one of chemosensitive tumors with high ability of nodal and extranodal spread and PET /CT is more sensitive than CT in monitoring response to treatment in non Hodgkin lymphoma diffuse large B cell type patients. Conclusions: PET/CT is the best tool for evaluation of the response to treatment in patients with Non Hodgkin lymphoma diffuse large B cell type, as well as Douveille criteria represent the accurate indicator of response categories determination.PET/CT has an obvious impact on clinical practice according to the response results and activity of residual lesion.